| With the gradual extension of China’s high-speed railway lines to cold regions,the problems of frost swelling and thawing and sinking of track subgrade soil caused by surface water infiltration are becoming increasingly prominent.Laying asphalt concrete subballast can improve the bearing capacity of subgrade bed and control the frost heaving and cracking of subgrade soil in cold regions.At present,the domestic research on the application of asphalt concrete for ballasted track mainly focuses on the material design of single-layer dense graded asphalt concrete to meet the requirements of waterproof layer and structural strengthening layer.Starting from the mechanical characteristics and functional requirements of ballasted track structure,this paper researches a composite asphalt concrete subballast composed of the upper large stone porous asphalt mixes layer with strong supporting capacity and the lower dense graded asphalt concrete layer with excellent waterproof performance,so as to give full play to the maximum efficiency of asphalt concrete in the foundation under ballasted track.The main work and conclusions are as follows:Based on the research of ABAQUS dynamic principle and viscoelastic material mechanics model,the dynamic model of composite asphalt concrete subballast is established by using the generalized Maxwell model.Comparing the measured data in the relevant literature,the reliability of the model is verified.By studying the spatial distribution of the dynamic response of the structure under the rail,the location of the dynamic analysis index is determined under the rail where the stress and strain are concentrated.Based on the finite element analysis,the results show that the laying of composite asphalt concrete subballast can reduce the vertical stress,vertical deformation and vertical vibration of the track structure.Compared with the single-layer dense asphalt concrete subballast with the same thickness,the results show that the laying of composite asphalt concrete subballast not only plays a good role in uniform stress,but also plays a more excellent damping function.It is found that the increase of ballast modulus will increase the overall stiffness of track structure,which is not conducive to the protection of subgrade structure;The increase of ballast thickness in the range of 25 cm ～ 35 cm can significantly reduce the dynamic response between the structural layers;The increase of the subgrade modulus will reduce the vertical deformation,vertical acceleration of each layer and the tensile strain of asphalt layer bottom,but will increase the vertical dynamic between the structural layers;The results show that the mechanical properties of composite asphalt concrete subballast perform better in low temperature environment,and the large stone porous asphalt mixes is more suitable for low temperature environment;Increasing the thickness of each asphalt layer is conducive to the reduction of the dynamic response analysis indexes,and the effect of changing the thickness of dense asphalt concrete layer on the tensile strain of each asphalt layer is more significant.According to the results of numerical simulation and field test,the main failure modes of asphalt concrete subballast during service are summarized.Considering of the environment,load and material parameters,checking process of structural design is formed with the indexes of low temperature cracking index,fatigue failure probability and saturated thickness.By this method,the structure of composite subballast is further checked.Finally,according to the use environment and functional requirements of asphalt concrete subballast,the dense asphalt concrete and large stone porous asphalt mixes are designed,and the high and low temperature,water loss resistance and mechanical properties of the mixture are evaluated.The results show that the designed composite asphalt concrete subballast structure can be well used as the foundation strengthening structure of ballasted track in cold areas. |
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